As seen in FIG. 1, modern optical communication and interconnection networks have a plurality of nodes 1 through 10, connected by optical fiber links 21 through 28. Communication networks are typically used for telecommunications and data communications, and interconnection networks are found in multi-processor computer systems.
Several information signals can be simultaneously transmitted on each optical fiber on different carrier wavelengths by modulating optical carrier signals with the information signals and combining the modulated carrier signals through Wavelength Division Multiplexing (WDM). In WDM, several modulated carrier signals propagate along a single optic fiber. The number of signals depends in part on the bandwidth of the network, including the optic fibers.
As the number of nodes increases, the cost of interconnecting the nodes also increases. To control these costs, techniques have been developed for obtaining communications between all nodes through logical connections, without having physical connections between every pair of nodes. As seen in FIG. 1, users may desire a communication topology that provides direct communication channels between communicating parties, as indicated by the dashed lines connecting the nodes. However, the underlying fixed physical network topology is limited to the links 21-28, and provides only indirect communication paths to those nodes. In other words, in FIG. 1, each of the nodes 1 through 10 can exchange data with every other node, but the only physical connections are the links 20 through 28. Nodes 3 and 4 can communicate directly with each other. Nodes 4 and 6 can also communicate, though indirectly, through the node 9. As a result, excessive network latency and congestion may arise.
In known optical systems, indirect communications between nodes are made by providing shared optical or opto-electronic switches at each node. Incoming signals are demultiplexed at each node, demodulated, amplified if necessary, switched and re-modulated on the same or a different wavelength carrier signal. The signals are then multiplexed with other modulated carrier signals, and transmitted on a selected outgoing optical fiber to another node. When there is heavy traffic, however, the processing delay in the switch fabric slows the delivery of information packets or frames, which are generally processed either on a prioritized or a first in, first out basis. Since both continuous high volume (i.e., high bandwidth) users and bursty low volume users share the same channels and wavelengths, switching delay is a major problem, especially for the high bandwidth users. Thus, there is a need for optical networks having improved optical switching systems in their nodes, for decreasing the switch delay or network latency in communication and interconnection networks.
Another problem with known optical networks is that a separate carrier wavelength is needed for each information signal, even if a particular information signal is only transmitted over a short part of the network. This is inefficient because it limits the total number of information signals, often sent in packets or frames, which can be transmitted over the network at any particular time. Thus, there is also a need to use networks more efficiently, by allowing more than one information signal to be transmitted on a single carrier wavelength under appropriate circumstances.
Accordingly, one object of this invention is to provide new and improved optical network communication and interconnection systems.
Another object is to provide new and improved optical networks which reduce switching delay and network latency by selectively switching signals directly through at least some network nodes.
Still another object is to provide new and improved optical networks in which more than one information signal can be transmitted on a single carrier wavelength by erasing one signal at its destination node and immediately reusing the carrier by modulating it with a second information signal in the same node.